The Invisible Monster
by Cravats are cool
Summary: Existence is a funny thing. Because, as long as you exist, no matter how unnoticeably, there's a chance you can help other people. There's a chance you can be seen. Featuring non-binary!Frisk and mute!Frisk.


Frisk twists and turns in their sleep, clutching at the sheets. Their lips are parted in a silent cry, and under their striped pajamas, they're covered in a cold sweat. The human grapples with their nightmare for a moment more, before waking up with a jerk. Immediately, tears start to prick at the child's eyes and they sniffle soundlessly. There's barely a night that goes by where Frisk doesn't have these nightmares, and there's little solace in waking up.

They can't seem to get their heart out of the Underground. Nightly, in their dreams, Frisk watches their friends turn on them, and has to fight their loved ones again. Then, for the rest of the night, they're stuck, dying over and over on a hellish loop until they wake up, reality greeting them with the old scars from their real fights.

Scuffing the back of their hand against their cheek, Frisk tries to push away the tears that are escaping. The child lets out a tight sob, thanking the stars that Toriel is a deep sleeper. For lack of anything better to look at, they direct their attention to the mirror on top of their dresser. In the glow of the moonlight, the battered human can stare back at themself. They look like a mess; with red, puffy eyes and snot running down their face. In spite of everything, Frisk is relieved that they can still recognize the human in the mirror.

In the reflection, Frisk spots a tissue box on their bedside table. They've can't recall having a tissue box in the house before. Puzzled, the child turns and takes a few. They wipe away their tears and manage to muster a smile for the human in the mirror. Once they're composed again, they dismiss the mysterious tissues as a gift from Toriel.

The convenience of that tissue box gives Frisk the determination to go back to sleep.

* * *

Far worse than the dreams where Frisk has to face their friends' wrath are the ones where they have to face their own. The tiny part of the child that wants to hurt others takes a form. The voice that they heard in the Underground, can still hear, encourages them to reset again and again. It's the chanting of a creature that Frisk is terrified will one day take over and destroy everything everyone's worked so hard for.

In the middle of the night, they awake from one of those dreams, on the verge of hyperventilation. Frisk scrambles out of bed. Careful not to make too much noise, they rush around their room and start to touch everything they can lay their hands on. It's the child's standard protocol after dreams like that; they check to make sure their room is still real. This particular night, the human is stopped short at the door. Their bedroom door is closed, but brightness shines through the crack at the bottom of the door. Quietly, they open it to confirm their suspicions; the light in the hallway is on.

Frisk knows that Toriel didn't leave it on; she says that she can't sleep with too much light. Consequently, the small human ignores their own fear of the dark and is sure to turn it off without complaint.

Absentmindedly, Frisk squeezes the side of door frame in a small hand, getting the chance to confirm their reality. Uncertain of the answer to this abnormality, the human goes back to sitting on the bed and reaches for a tissue. Frisk blows their nose quietly, trying not to wake their mother. From the bed, they stare at the light until their eyes hurt, forcing themself to push the dream out of mind.

Soothed, the human manages to fall asleep once more.

* * *

A week after the incident with the lights, Frisk has another nightmare. They struggle so much that they fall out of bed and wake up when they hit the ground. They can't remember what the nightmare is about, but they're trembling when they stand up. The child spots a glass of water on their bedside table and gulps it down. It's the middle of the night; by all rights the water should be warm, but for whatever reason it was ice-cold.

Things seemed to be going well for Frisk, recently. Random little unexplained things, like the pretty wildflowers that would sometimes show up at their door, or an object stolen by the Annoying Dog turning up out of the blue. The human's bed is always made, no matter how messy it was, and Toriel swears upside-down and backwards that it wasn't her. Stranger still, any kid that pushes Frisk around at school winds up later with gum in their hair or their homework torn up.

Needless to say, the child no longer questions when things like a glass of cold water appear without reason.

Frisk sets aside said glass. They stare at their hands, taking deep breaths to keep from panicking. They see a flicker of motion over near the window.

There's a splotch of light shining on the bedroom wall, streaming in from the hallway. If Frisk pays attention, they can see shadows dancing near the bottom of the wall in the light. Fright put away in favor of curiosity, the young human looks around for the thing casting the shadows. They can't find it. Brow furrowed, they scan a second time, then a third. There's nothing there.

The shadowy movements on the wall quicken, blurring together. But when the child inspects the motions very carefully, they find that it's all very familiar. It's sign language. The signer is going very fast, but the human thinks that they catch the words "child," "water," and "help."

Inspired, Frisk roots through their desk to pull out a flashlight. They turn it on and position the beam so that it's just above the other patch of light. Certain they had the other's attention, the human starts to sign.

 _Hello._ They wave. There. Best to start it off simple.

Beneath the light from the child's flashlight, the shadowy motions stop dead. There's a long pause, in which Frisk worries that they frightened the other off, before-

 _YOU… YOU CAN SEE ME?_ Unlike the signer's prior swift movements, these are hesitant, shocked.

Checking one last time for any signs of someone else in the room, Frisk finds nothing. _No,_ they sign back. _I can see what you're saying, though. It's up on the wall._

There's another lengthy pause, and Frisk really wishes the other would stop doing that. After about thirty seconds, they receive an, _OH._

 _So, why can't I see you?_ They're starting to get excited now; the thrill and slight fear that comes with talking to a stranger late at night. _Are you a monster? A super small monster?_ The child dangles their legs off the bed while they wait for a response.

 _SOMETHING LIKE THAT._

That means that they aren't right. The child frowns. _Or, are you invisible?_

 _THAT'S A BETTER WAY TO PUT IT._

 _Must be cool._ Frisk smiles. _I wish I were invisible sometimes._

 _DON'T._

The smile fades off of the human's face. They don't have anything to say to that. And the invisible monster doesn't make any stabs at conversation either. They sit in silence while the pieces fall into place in the child's brain.

 _So…_ This time, Frisk is the one to hesitate, _Have you been the one doing all of those things for me? The tissues, the lights, the gum in Debbie's hair?_

 _YES._ The delivery is flat, not expecting any commendation. Which is good, because Frisk isn't about to throw praise at this monster's feet. Assuming that he has feet.

Instead, they ask, _Why?_

 _I DON'T HAVE ANYTHING BETTER TO DO,_ comes the blunt answer. There's an echoey chirruping noise from somewhere in the room. It manages to sound somewhat bitter. _I DON'T HAVE ANYTHING TO DO AT ALL._

Frisk doesn't quite believe that's the whole truth. But they're a helper. To everyone. And, though they can't even see this invisible monster's face, they feel bad for him. They're already resolving to find ways to encourage him. They nod to themself, looking fierce, and sign, _What's your name?_

 _G-A-S-T-E-R,_ The invisible monster spells out.

 _G-A-S-T-E-R,_ Frisk signs it back to him, letter-by-letter, before stringing together the motions for "helpful," "shadow," and "monster" quickly into his sign name. _My name is F-R-I-S-K._

Gaster doesn't protest Frisk's name choice for him, but nor does he bother giving the human a sign name of their own. _I ALREADY KNOW._

 _Well, Gaster,_ they ignore him and use his sign name again, _now you can talk to me. And if you want to do things like get me water and make my bed every day, I won't complain!_ They smile brightly at wherever he is, assuming that he can see them.

… _.RIGHT._ Gaster seems taken aback.

 _We can be friends!_ The child gives the empty room friendly, possibly flirtatious finger-guns for good measure.

 _FRIENDS?_

Frisk nods. They start to lie back down and pull the covers over themself. _Just you wait. We'll be friends._ They won't take no for an answer.

The invisible monster doesn't respond for a moment, clearly at a loss for words. The human spares him from having to come up with an answer. _Goodnight, Gaster,_ they sign, flicking off their flashlight and flipping onto their other side. They can sense they won't have any problems with nightmares for at least the rest of the night.

Though the human can no longer see, the invisible monster responds. _GOODNIGHT, F-R-I-S-K._ Gaster pauses before coming up with a sign name. It involves a double patting motion, putting the tips of a vertical left index finger and holding the other horizontally to make a corner, and then forming two fists, crossing arms over one another. All together, it means "child to protect."

 **Author's Note: I don't actually speak ASL, please correct me if I described anything wrong. Gaster has literally zero canon personality, so this was hard. Also, this is my first (technically second, but I'm saving posting the other one until Valentine's Day) fanfic for this fandom, so please drop a comment or a fave for feedback, so I can scream about this fantastic game with you, and meet new people. Thanks for reading!**


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